1. Technical Field
The invention is related to a method of using test equipment for obtaining an optimum focus of an image viewed by an electro-optic sensor system under test.
2. Background Art
Electro-optic sensors such as FLIR sensors (forward looking infrared sensors typically include an infrared detector plane consisting of an array of infrared-detecting diodes in an integrated circuit and an optical system constituting an assembly of lenses and filters for directing light from a field of view onto the array.
It is very important that such devices be accurately characterized upon completion of their manufacture before they are used in the field. Typically, a great investment must be made in post-production test equipment to test electro-optic sensors. Such test equipment measure numerous system parameters such as dynamic range, modulation transfer function, minimum resolvable temperature difference and field of view. Before performing these tests, the operating point of the sensor must be determined. This is done by optimizing the sensor's contrast, brightness and focus relative to some test image viewed by the sensor. Locating best focus is critical to achieving accurate results for tests such as those mentioned above. Best focus is traditionally determined by viewing the video display of a resolution chart in the field of view of the sensor while manually varying the focus of the sensor until the human operator observes that an optimum sharpness has been achieved. This is a subjective process. Determination of best focus by this method may vary from test to test and observer to observer. What is needed is a purely objective way of determining the focal length of an electro-optic sensor under test.